Interest in alternative energy sources has resulted in growing numbers of solar collector installations, heat pumps, wood burning furnaces and boilers, etc., as sources of heat energy. Typically, heat energy is stored in heated water for subsequent use. An important component of such systems is therefore an insulated tank for example in the form of a 100-500 gallon (380-1,904 liter) metal tank wrapped with appropriate insulation or larger tanks built in place at the site. Such tanks add substantial expense to the system installation and are difficult to transport and locate in a building. For example, for a large tank, adequate clearance is necessary in entryways and frequently the tank cannot be installed at the preferred location.